This invention relates to a sputtering target used with a sputtering equipment and ion-milling equipment, and more particularly to a sputtering target in fabricating a film consisting of two or more components.
At present, the gate electrode of an MOS LSI device is generally prepared from polycrystalline silicon. When, however, it is attempted to develop a high speed MOS LSI device, a high sheet resistance of a polycrystalline layer presents a great hindrance. Even when a polycrystalline silicon layer is fully doped with an impurity, the lower limit of the specific resistance of said silicon layer is around 10 .OMEGA..quadrature.. It is impossible to reduce the specific resistance to a lower extent that said level.
Recently, therefore, it is widely accepted to prepare the gate electrode of the MOS LSI device from a silicide of refractory metal of low specific resistance such as molybdenum or tungsten. A film of such refractory metal silicide is generally formed by the process of vacuum thermal deposition or chemical vapor deposition (CVD). However, this sputtering process is more widely accepted which ensures the easy formation of such film. A refractory metal silicide film formed by the sputtering process is carried out by applying a target prepared from refractory metal silicide by a sintering process. However, this target prepared by the sintering process is difficult to be highly purified, greatly obstructing the formation of the gate electrode of the MOS LSI device.
Refractory metal and silicon can respectively be highly purified in the single form. To date, therefore, a target constructed, as shown in FIG. 1, by mounting a plurality of silicon strips 2 on a refractory metal substrate 1 has been subjected to sputtering to produce a refractory metal silicide film. In this case, it is obviously possible to produce a target by mounting strips of refractoy metal on a silicon substrate.
The sputtering process applying the target constructed as shown in FIG. 1 has the advantage of fabricating a refractory metal silicide film with great ease and high purity. However, the sputtering process of FIG. 1 which involves the application of a target constructed by mounting a plurality of silicon strips 2 on a refractory metal substrate 1 has the drawbacks that abnormal discharge is likely to take place along the edge of the silicon strips 2, resulting in the variation of the composition of an intended refractory metal silicide film or tending to give rise to the splashing of the fine particles of the target materials of the target. Further, the target of FIG. 1 is only applicable to the sputter-up process (in which the target is held in a lower position and a substrate on which a refractory metal silicide membrane is to be deposited is kept in an upper position). However, the target of FIG. 1 presents difficulties when it is applied not only to the sputter-down process but also to the side-sputter process capable of effectively suppressing the contamination of the refractory metal silicide film during its formation (said side-sputter process is carried out with the target and substrate made to face each other perpendicularly). The reason is that the silicon strips 2 disposed on the refractory metal substrate 1 tend to fall off.